1. Field of the Invention
The present invention relates to a computer system and more particularly to a computer system which allows option controller cards for various input/output (I/O) devices to be added on the motherboard at minimum cost.
2. Description of the Prior Art
The modern microcomputer must be capable of supporting a wide audience of users from the hobbyist to the corporate power-user. This requires that the computer must support a wide array of peripherals which might include LANs, modems, disk controllers, video controllers, or multimedia controllers. If the general purpose microcomputer is to address this large audience economically, it must provide these functions as options to a minimally configured basic machine.
One solution to this problem is to provide multiple industry standard bus slots such as ISA, EISA, MCA, or NuBUS, which the user can use to install a third party peripheral controller. The addition of these slots requires the system cabinet to be large and bulky. The power supply must also be capable of supplying the worst case power required for each slot, multiplied by the number of slots available.
With the current level of integration available today these peripheral functions can often be provided using a single LSI device along with several small support devices used for address decoding, resource routing, data buffering and interfacing. This amount of circuitry can easily fit on the smallest, industry standard, bus card and still have room to spare. However, regardless of the minimum physical size of the logic required to implement the function, the user must sacrifice one of the, typically few, standard bus slots designed into the computer. Since the manufacturer of the computer had to provide enough space and power to support the worst case (largest) card that could have been installed into the standard slot, the user ends up paying more than was needed for the extra capability that has not been used.